This invention relates to a front plate to be disposed on the front of a plasma display panel (hereinafter sometimes referred to as PDP) and method of producing the same, and more particularly to a front plate for plasma display panels, with the component members fast adhering to each other, easily produced by a process comprising simple steps and excellent in productivity, and method of producing the same,
It is reported that large quantities of harmful electromagnetic waves of non-ionized ray, e.g., microwaves and radio waves, are emitted from surfaces of displays, e.g., those for a variety of computers (e.g., office and factory automation devices), game machines and TV sets. Recently, adverse effects of these electromagnetic waves on human health have been pointed out, and their interference with other devices gives rise to other problems.
More recently, a plasma display panel (PDP) as light-emitting, planar display panel has been attracting attention as a large-size display excellent in visibility. However, the PDP emits more intense electromagnetic waves leaking out of the front face than the conventional display panel, e.g., cold-cathode ray tube (CRT) or liquid crystal display panel (LCD), and hence is strongly required to have a better electromagnetic shielding function. Moreover, the PDP emits, from the front face, near-infrared ray derived from inert gas, e.g., Ne or Xe gas, contained in the cell. The near-infrared ray has a wavelength close to the wavelength at which remote controllers operate for a variety of home electronic devices, and hence may cause malfunction of these devices. Therefore, the PDP is also strongly required to have a function of sufficiently shielding the near-infrared ray. Furthermore, it is required to have anti-reflection and anti-dizziness functions to improve image quality and visibility, and prevent flickering of the screen.
As described above, the PDP is strongly required to have various functions, e.g., those for shielding electromagnetic waves and near-infrared ray, anti-reflection, and anti-dizziness, depending on its purpose and service types. The front plate adequately provided with some of these functions has been widely used and disposed on the front face of a display panel, in order to satisfy these requirements.
The front plate for PDP""s is required to have these functions as a whole, and is generally composed of two or more component members each having one or more of these functions. One of the typical examples comprises a transparent substrate, e.g., glass or acrylic plate, orderly coated with members, e.g., electromagnetic shielding or electroconductive member, near-infrared ray absorbing or reflecting member, and anti-reflection or anti-dizziness member, depending on the required functions. When these component members are formed into a monolithic structure, it is advantageous to bond the two members to each other under heating at elevated temperature and pressure with an adhesive layer in-between, because it can bond these members to each other in one stage. As such, this method, wherein an adhesive film is put between the two component members, is generally followed.
For the front plate for PDP""s to have two or more of the above-described functions, it is necessary to coat the transparent substrate with films each having one or more of the functions on one or both sides, normally by hot pressing. In such a method, however, the number of film adhering steps increases as the number of required films increases, causing notably deteriorated productivity and increased production cost.
Moreover, when each of the component members for the front plate for PDP""s is required to be large in size and satisfy the specifications more strictly, only a slight deviation in setting before the hot pressing may cause significant problems after these members are assembled. When a heat-bond type film is placed between the component members, in particular, each member tends to move to cause deviation while being set, and more careful setting to prevent the deviation needs much more time and labor.
For the front plate for PDP""s with the component members adhered to each other via a heat-bond film, they are commonly assembled into the monolithic structure at elevated temperature. One of the major problems associated with such an assembly is thermal deformation of the optical film as the outermost layer to generate a strain, which can deform the optical film surface and produce fine irregularities on the surface to deteriorate its smoothness. These problems, in turn, cause quality-related problems, e.g., unclear or distorted PDP images through the front plate.
Another type of problem resulting from forming at elevated temperature is thermal shrinkage of the surface optical film, which can warp the front plate as a whole, preventing its smooth setting of a PDP.
Still another type of quality-related problem resulting from forming under severe conditions of elevated temperature is deterioration or alteration of a chemical substance given to the optical film for a function, e.g., near-infrared shielding function, with the result that the front plate may no longer fully exhibit the function.
In order to solve these problems, various types of front plates and front filters for plasma display panel (PDP) have been proposed. For example, Japanese Patent Laid-Open No.330660/1997 discloses a front plate for PDP""s which uses a panel comprising a transparent resin plate coated with an electroconductive substance on one side. Japanese Patent Laid-Open Nos. 352318/1999 and 28813/2000 disclose a monolithic assembly with a transparent resin plate and film bonded by hot pressing to each other via an adhesive layer, wherein the film is of polyester or polycarbonate. Japanese Patent Laid-Open No.292575/1999 discloses a monolithic assembly with 2 transparent substrates bonded to each other via an electroconductive mesh as the intermediate layer for bonding.
These proposals, however, have failed to produce the front plate for PDP""s free of the above problems, i.e., the front plate excellent in processability for forming a monolithic structure, with each component member resistant to deformation or warping, easily produced by a simple process, and excellent in productivity. Therefore, there are strong demands for development of the front plate for PDP""s excellent in functions of, e.g., shielding electromagnetic waves and near-infrared ray and anti-reflection, and free of the above-described problems.
It is an object of the present invention to provide a front plate for plasma display panels free of the above problems involved in the conventional front plate, with the transparent substrate, electroconductive member and optical film fast adhered to each other, easily produced by a simple process, and excellent in productivity. It is another object of the present invention to provide a method of producing the same.
The inventors of the present invention have found, after having extensively studied to solve the above-described problems, that the quality-related problems of the conventional front plate for plasma display panels result from the severe conditions of elevated temperature and pressure under which the component members are assembled into a monolithic structure, and that these problems can be solved by orderly placing two types of adhesive layers of tackifier layer and heat-bond film between the optical film and the adjacent member to press them under heating, when a monolithic assembly of transparent substrate laminated with an electroconductive member and at least one type of optical film is produced, because the component members can be assembled under lower temperature and pressure to give a desired front plate for plasma display panels. This has led to development of the present invention.
The first aspect of the invention provides a front plate for plasma display panels comprising a transparent substrate laminated, at least on one side, with an electroconductive member and at least one type of optical film to form a monolithic structure, wherein
(a) two types of adhesive layers of tackifier layer and heat-bond film are orderly placed between the optical film as the outermost layer and the adjacent member, and
(b) the transparent substrate, electroconductive member and at least one type of optical film are pressed under heating.
The second aspect of the invention provides the front plate for plasma display panels of the first aspect of the invention, wherein thickness of the two types of adhesive layers is defined by the 10 to 50 xcexcm thick tackifier layer and 50 to 250 xcexcm thick heat-bond film.
The third aspect of the invention provides the front plate for plasma display panels of the first or second aspect of the invention, wherein the optical film has at least one of the functions selected from near-infrared ray shielding, anti-reflection and anti-dizziness functions.
The fourth aspect of the invention provides the front plate for plasma display panels of the third aspect of the invention, wherein the optical film further has a color-correcting function.
The fifth aspect of the invention provides the front plate for plasma display panels of the third or fourth aspect of the invention, wherein the near-infrared shielding function is kept by the film of transparent resin dispersed with a near-infrared absorbing colorant, or a combination of near-infrared absorbing colorant and color-correcting pigment.
The sixth aspect of the invention provides the front plate for plasma display panels of the fifth aspect of the invention, wherein the transparent resin is polycarbonate.
The seventh aspect of the invention provides the front plate for plasma display panels of one of the first to sixth aspects of the invention, wherein the electroconductive member is an electroconductive fiber mesh.
The eighth aspect of the invention provides the front plate for plasma display panels of one of the first to sixth aspects of the invention, wherein the electroconductive member is an electroconductive metal net.
The ninth aspect of the invention provides a method of producing a front plate for plasma display panels, comprising a transparent substrate laminated, at least on one side, with an electroconductive member and at least one type of optical film to form a monolithic structure, wherein
(a) two types of adhesive layers of tackifier layer and heat-bond film are orderly placed between the optical film as the outermost layer and the adjacent member, and
(b) at least one type of adhesive layer of tackifier layer or heat-bond film is placed or not placed between the members except those of (a) above, and
(c) the transparent substrate, electroconductive member and at least one type of optical film are pressed under heating.
The tenth aspect of the invention provides the method of the ninth aspect of the invention, wherein the pressing under heating is effected at 80 to 120xc2x0 C.